/Engine/Plugins/Online/OnlineSubsystem/Source/Public/Interfaces/OnlinePartyInterface.h
Notification when a party is joined
typedef TMulticastDelegate_TwoParams< void, const [FUniqueNetId](API\Runtime\CoreOnline\Online\FUniqueNetId) &, const [FOnlinePartyId](API\Plugins\OnlineSubsystem\FOnlinePartyId) & > FOnPartyJoined